The present invention relates to a planar waveguide having optical nonlinearity and particularly to one which makes use of ultraviolet excitation poling.
With recent advances in information processing technology involving computers and the like, the need and desire to process and transmit massive amounts of data (mass-data) at high speeds have increased. Currently, optical fiber transmission is the most effective means for mass-information transmission and has become widely used.
Optical fiber transmission works by transmitting optical signals through optical fiber. In order to transmit signals through optical fiber, elements such as a light source, a light receiving element, an optical signal generator, an optical switch/coupler, transmission optical fiber, and the like are necessary. An electrooptical effect (optical nonlinearity, a phenomenon which results from nonlinear polarization generated in a substance by light) is then used for an optical functional element such as an optical signal generator, an optical switch and the like. Therefore, an optical switch element and the like are produced by controlling electric field strength applied to an optical nonlinear material to change intensity or direction of light transmitted into the optical nonlinear material.
Optical fiber transmission of information can be achieved by applying optical modulation to light introduced into the optical fiber on the basis of information to be transmitted by making use of an optical functional element and then demodulating the light signal on the light-receiving side.
Crystalline materials such as LiNbO3, BaTiO3 and the like are now commonly used as an optical nonlinear material because there are, at present, no other materials that can realize sufficient nonlinearity.
On the other hand, from the standpoint of stable connection with glass-made optical fiber, low losses in transmitted light, reduction of cost, wide range of transmitted wavelength and the like, it is preferable to construct an optical functional element such as an optical switch or the like from a glass material.
Accordingly, attempts have been made to impart optical nonlinearity in glass materials. For example, ultraviolet excitation poling by irradiating a glass material with ultraviolet light in a state where high electric field of approximately 106 V/cm is applied is described in xe2x80x9cELECTRONICS LETTERS Mar. 30, 1995 Vol.31 No.7 pp.573-574xe2x80x9d.
It is believed that ultraviolet excitation poling is able to impart to a glass material optical nonlinearity equal to that of a crystalline material, which may then be preferably used as an optical functional element.
Although according to the conventionally proposed ultraviolet excitation poling described above, nonlinearity may be given to the glass materials, that nonlinearity is given only to a definite area of the core of the optical fiber. Therefore, only the possibility of availability for an optical functional element is shown.
Further, although an optical fiber optical functional element has additional advantages such as simple connection for transmission, functions are limited and shape dependent. On the other hand, a planar waveguide is also able to form plural waveguides, and a diversification of processing function may be attempted. It is considered that if optical nonlinearity may be given to the glass-made substrate, a planar waveguide preferable for various applications can be obtained.
The present invention has been achieved in light of the aforementioned problems and its objective is to present a process for producing a planar waveguide by giving optical nonlinearity to a glass-made substrate to realize a planar waveguide having optical nonlinearity.
The process for producing a planar waveguide according to the present invention is characterized in that a pair of electrodes of conducting material is arranged at a gap corresponding to core area of waveguide on the surface of the glass-made substrate and the surface of the glass-made substrate is irradiated with ultraviolet light through said gap in a state where voltage is applied between these electrodes so that ultraviolet excitation poling is applied to the core area.
According to the present invention as outlined above, an optical nonlinearity is introduced to the core area of the surface of the glass substrate by applying the ultraviolet excitation poling thereto. Therefore, a variety of functions can be effected by controlling the electric field applied to the core area having the optical nonlinearity. Further, since the nonlinearity can be given to only a part of the glass substrate, such effects as low cost, easiness of connection with glass-made optical fiber and the like can be obtained. Particularly, since the nonlinearity coefficient more than several P m/V similarly to that of LiNbO3 can be obtained according to the ultraviolet excitation poling to the glass, and its response to electric field becomes sufficient for application.
The present invention is also characterized in that a step for forming a conducting metal film on the surface of the glass substrate, a step for etching the metal film thus formed to form a pair of electrodes at a determined gap, a step for introducing specified atoms in the surface of the substrate under the aforementioned gap using the electrodes thus formed as masks to form core area, and a step for irradiating the core area with ultraviolet light in a state where voltage is applied between the pair of electrodes to effect ultraviolet excitation poling are completed to give optical nonlinearity to the core area.
As described above, by forming the core area after the metal film is etched, the core area can be formed under the gap between the electrodes, and the ultraviolet excitation poling can be easily and certainly applied to desired area of optical waveguide.
The present invention is further characterized in that the irradiation with ultraviolet light to the aforementioned core area is carried out through a given phase mask, and parts having optical nonlinearity are formed periodically in the core area.
As described above, gratings can be formed in the core area by discontinuous irradiation with ultraviolet light. Light of a specified wavelength (Bragg wavelength) can then be reflected and interfered by these gratings. As the Bragg wavelength varies according to applied voltage, it is possible to make the core area operate as, for example, a wavelength switch.
In particular, according to the present invention, the gratings can be easily formed using a simple process of limiting the area to be irradiated with ultraviolet light using a phase mask.
The planar waveguide of the present invention can also be characterized by its inclusion of a glass substrate, a pair of electrodes formed on the substrate through a determined gap, a core area which is formed on the surface of the substrate under the gap between the pair of electrodes and the refractive index of which is different from that of the substrate by addition of specified atoms, and the aforementioned core area being given optical nonlinearity of 1 pm/ V or above as the electro-optical coefficient.